Human tear protein fractions during waking hours.

Reliable collection and analysis of human tear proteins presents considerable problems. The volume of unstimulated tear samples is necessarily very small, although stimulated tears may be easily provoked with a consequent change in composition. In the present study, 5-microliters samples of human tear fluid were carefully removed, over a 10 min period, from 10 male Caucasian subjects with the aid of a 5-microliter "microcap". The procedure was repeated at 2-h intervals between 08.00 and 22.00 hours. The collected samples were individually separated into their major protein fractions using gel column electrophoresis. The separated material was stained and scanned, and the concentration of proteins present estimated by comparison with known protein standards. Consistent values for protein concentrations were recorded for all participating subjects, and no variation during waking hours was demonstrated.